So you have the free game C-evo on your computer? Click the appropriate icon or file and you should get a screen with a pretty logo at top right and a mostly gray useful rectangle at bottom left.
Tabs on the rectangle are "Map", "New Book", and "Earlier Books".
"Map" takes you to a list of available maps, from which you may select. Closing the map returns you to the main screen with the chosen map indicated in the multi-colored minimap on the right of the rectangle.
"New Book" is what you use to start a new game. You can set the number of foreign nations, up to 14 (unless you are playing a scenario that sets a different number). You can set the level of difficulty, in five classes ranging from Beginner to Insane. You can set the end date (2400 AD being the default).
Clicking "Free Player Setup" allows other options, where you can specify the level of difficulty for each nation (from one bar - about 25% easier than standard - to three bars - 25% harder) and can specify which AI will be used.
When done with that rectangle, click "Start" and choose your tribe. The standard list is Americans, Babylonians, British (all with English city names, no Scots or Welsh!), Chinese, Egyptians, French, Germans, Greeks, Japanese, Mongols, Persians, Phoenicians, Romans, Russians, Spanish, Vikings. Some of the standard colors are hard to distinguish: if you want a distinctive one, choose Persians or Spanish.
Clicking after you choose your tribe brings you to the start of the game, where (after you click OK to the introductory message) your new size-4 capital city is displayed with the 21 tiles you know about and a blinking Settler unit on one of them ready to start work or move. If there is ocean within sight, you may see part of your territory border. Click on the city to see what it is proposing to build and which tiles are being worked. Note that one of the population works the city tile, unlike how some other games work.
From this point on, the wiki has several guidance pages, mostly in Category:Guides (C-evo).